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Chemical Signals in Animals � Chapter 45 � The Endocrine System

Hormone � is a chemical signal that is secreted into body fluids (blood) and communicates regulatory messages within the body

Target cells � respond to hormones

Two systems of internal communication and regulation nervous system and endocrine system




Nervous high speed signals along neurons … movement in response to env changes

Endocrine all of an animal’s hormone secreting cells … endocrine glands hormone secreting organs (ductless glands � directly into body fluids)

Endo and nerv are structurally, chemically, and functionally related

-endo organs contain nerve cells called NEUROSECRETORY CELLS … secrete hormones … many chemicals = signals in nervous system, hormones in endocrine sys …

-each system affects the output of the other .. release of milk suckling = sensory cells - nervous signals - hypothalamus - oxytocin from pituitary - secrete milk

Invertebrates hormones = reproduction and development … nerve and hormne interaction …

-Arthropods crustaceans growth and repro, water balance, movement of pigments, reg of meta … aquire adult characteristics in single, terminal molt .. molting is triggered by ECDYSONE … also favors development of adult characteristics (cater - butter) … ecdysone production is controlled by nd hormone brain hormone (bh) … stimulates prothoracic glands to secrete ecdysone

-balanced by juvenile hormone (JH) . secreted by corpora allata … propotes retention of larval characteristics … high JH = molting but just larger larva … low JH = pupa - metamorphosis …

local regulators � act between cells on a localized scale … upon release taken up by target cells, broken up by enzymes, or hend by extracellular matrix � thus, can only affect local targets .. Pheromones � carry messages between different individuals of a species … ie mate attraction …

local regulators neurotransmitters one neuron to another, or one neuron to muscle, gland …

Nitric oxide (NO) � multiple functions … highly reactive/toxic … affects targets in few seconds and breaks down … secreted by neurons …. Funct as a neurotransmitter .. secreted by white blood cells � kills cancer cells and bacteria in bf … sec by endothelial cells in blood vessels � makes smooth muscle relax, dilating vessel walls

-Growth Factors � peptides and proteins that fuction as local reg … each can affect several types of cells and have variety of functions … Nerve growth factor NGF � speeds rate of developing white blood cells

-epidermal GF � accelerates epid development … Insulinlike GF � skeletal development (produced by liver) … transforming GF � enhance the strength of synapses between neurons in brain of mature animal

-Prostaglandins PGs - modified fatty acids derived from lipids of pm … in semen promote contractions of uterus …

-released by cells into interstital fluid � func as local regulators … sec by placenta = changes in chem. Of uterus = induce labor (positive feedback) …

-defense mech induce fever and inflammation … intensify pain … ^Aspirin inhibits enzymes to synthesize prostagladins

-PGE and PGF � similar structures but different effects on smooth muscle cells of blood vessels serving lungs … PGE = relax (dilate blood vells, promote oxygenation) … PGF = contract (reduce blood flow) … thus antagonistic …

chem. Signal can affect different tcells diff or diff species diff … ie thyroxine vertebrates metabolic reg … and development … ie frog from tadpole …

-modes of action of all chem. Sig are similar … each sig has specific shape to be recog by tcells … binds to receptor receptor in pm or inside tcell … signal molecules are ligands small molecule that bind specifically to larger ones (proteins) … triggers chem. Events .. result in change in behavior of cell … diversity of responses depends on nature of tcells and # and affinity of receptor proteins on/in cells …

bind to pm � signal trasnduction pathways … melanocyte-stimulating hormone MSH (peptide hormone secrted by pituitary) … melaoncytes specialized skin cells containing dark brown pigment melanin in cyto organelle called melanosomes … skin appears light when melano are clustered tightly around nucleus … darker when spread … MSH secreted = disperse … direct injection into cells does nothing

-most chem. Signals ( neurot, gf, hormones) unable to pass through pm … instead are components of signal transduction pathways …. Convert extracellular chem. Sig into specific response … changing behavior of cell …. Stp trigger enzyme cascades that amplify the hormonal signal

most steroid receptors and receptors of thyroid hormones and some local receptors (NO) are specialized proteins within target cells … enter target cells … bind with receptors … activate receptor … response

-hormone-receptor complex binds to specific sites on DNA .. transported into nucleus, attaches to reg sites along genome … transcrp of gene into mra … trans into protein … hr complex binding to these sites can induce or suppress expression of spe genes … ECDYSONE � steroid … triggers synthesis of enzymes that catalyze new exoskel … estrogen induces female bird repro cells to syn ovalbumin (storage protein in egg white)

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